Quantification of Point Defect Energy in MDACl2-Stabilized Perovskite Solar Cells
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Date
2020
Authors
Wales, Nicole
Crawford, Zack
Lonergan, Mark
Journal Title
Journal ISSN
Volume Title
Publisher
University of Oregon
Abstract
Perovskite solar cell efficiency is reduced by Shockley-Read-Hall (SRH) recombination, in which charge carrier collection is diminished by the presence of sub-band gap energy states, called traps. Theoretical studies have credited some crystallographic point defects with the production of such states. By understanding how these defects form and contribute to a material’s electronic structure, we will gain insight into routes of SRH recombination and the related loss of efficiency. Thus, we aim to measure and describe the nature of formation of traps in real materials. External quantum efficiency measurements are used to extract a Gaussian distribution of trap states. Capacitance techniques enjoy enhanced sensitivity to traps in the absorber layer, however, are accompanied by complications associated with the hysteretic perovskite system. Methylenediammonium dichloride-stabilized alpha-formamidinium lead triiodide perovskite contain interstitially incorporated chloride ions and have impressive power conversion efficiencies of 23.7%, leading to their use in this study. EQE spectra of MDACl2-stabilized samples gave a small defect signal with transition energy of 1.08 ± 0.01 eV. Findings may point to material suppression of sub-gap defects associated with MDACl2 – stabilization compared to alternative compositions.
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Keywords
Perovskite, Photovoltaics, Defect Trap States, EQE, Shockley-Read-Hall recombination